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We propose the design of a flat active wall panel and demonstrate its effectiveness in modulating the wall impedance, which can lead to the total absorption of incident sound waves in the low-frequency range of 50--120 Hz, or alter its reflection phase. Such an acoustic frequency range is usually the most difficult to handle for passive acoustic components, owing to the long wavelength, and consequently, the bulky size of the materials required. The active panel is actuated by a piezoelectric transducer, with its vibrational displacement amplified by a specially designed mechanical amplifier. Through both simulations and impedance-tube experiments, we show that simply tuning the active panel's displacement amplitude can vary its impedance from that of the hard wall, to impedance matching with air (leading to total absorption), to zero (leading to reflection phase reversal). No feedback loop is necessary for the active-panel device; only an initial adjustment during installation is necessary. We simulate the room-acoustics application for a 1 1 m^2 wall panel that occupies only 1/48 of the total wall area of the room and show that it can introduce switchable elements to the audio experience.
Gao et al. (Wed,) studied this question.